Performance enhancement of recycled aggregate concrete (RAC) incorporating pre-soaked recycled concrete aggregate (RCA) and silica-based additives

Recycled aggregate concrete (RAC) offers a sustainable alternative to conventional concrete, but the limitations of recycled concrete aggregate (RCA) constrain its structural use. This study examines the effects of micro-silica (MS) and nano-silica (NS) on the mechanical performance of RAC incorporating presoaked RCA. Two reference mixes (dry and soaked RCA) were prepared to isolate the soaking effect. Eight additional mixes were designed by varying MS (5 %, 10 %) and NS (1 %, 2 %, 2.5 %) dosages. The mix with 5 % MS and 2.5 % NS achieved the highest compressive strength (+44.6 %) and elastic modulus (+17.8 %). The maximum improvement in splitting tensile strength (+32.5 %) was observed at 5 % MS and 1 % NS. Slump and density tests confirmed uniform dispersion and acceptable workability. SEM and EDX analyses revealed denser ITZ and improved silica distribution. Results demonstrate that combining MS and NS with presoaked RCA significantly enhances RAC properties, supporting its structural application in sustainable construction.